Boiling is used when disinfecting compounds are not available. It is a good method for killing disease producing organisms, but has several disadvantages.
1. Fuel is required.
2. It takes a long time for the water to boil and then to cool.
3. There is no residual protection against recontamination.
4. The water must be held at a rolling boil for at least 15 seconds to make it safe for drinking.
Five-gallon cans of water may be disinfected as follows:
1. Fill the 5-gallon can with the cleanest water available.
2. Check iodine tablets for physical change.
3. Dissolve 20 iodine tablets in a canteen cup full of water. Add this solution to the 5-gallon container and agitate the solution. 4. Place the capon the container loosely; wait 5 minutes, then again agitate the container well.
5. Tighten the cap and wait an additional 20 minutes before using the water for any purpose.
When treated water is not available, small groups of personnel can treat an emergency water supply by chlorinating water in a Lyster Bag. Lyster Bags are 36-gallon containers issued to units on the basis on one bag per 100 men. The porous canvas, of which the bags are made, allows seepage of water and thus cooling by evaporation.
Unfortunately, the canvas is organic matter that has a chlorine demand of its own and makes it difficult to maintain adequate levels of chlorine. The bag is suspended from ropes or poles. Sagging can cause the outlets at the bottom of the bag to drop onto the ground below the bag. Should this occur, the rope should be adjusted so that the cover will again fit snugly around the upper part of the bag and the spigots will be at least 18 inches above ground level. Proper adjustment of the cover prevents contamination of the water by dust, dirt, and insects. The bag must be inspected 11-37 frequently for cleanliness and chlorine residual. If the bags are dirty, they should be scrubbed with water, disinfected, and thoroughly rinsed.
1. Fill the bag with the clearest water available.
2. Initially take 2 ampules of 65 to 70 percent calcium hypochloride (HTH) and pour the contents into a canteen cup. Add approximately 4 to 6 ounces of water to the cup and stir the solution thoroughly. Allow the solution to settle for several minutes (approximately 5 minutes) so the insoluble portion will settle to the bottom of the cup. Then stir the clear, supernatant liquid into the Lyster Bag.
3. Flush the faucets; wait 10 minutes, and collect the water sample. If it is less than a 5.0 ppm free available chlorine residual, repeat step 2 above.
4. Continue repeating the disinfection procedure until a 5.0 ppm residual is obtained after 30 minutes of contact time. The water is ready for use.
Potable water for shipboard use comes either from the sea through the ships evaporators, from another ship, or from sources ashore. The ships medical department is responsible for determining the quality of the water; the engineering section determines the quantity stored or produced and does the actual chlorination or bromination.
Potable water obtained from an area where amebiasis or hepatitis is endemic must be chlorinated or brominated to obtain a 2.0 ppm residual in the tanks following a 30-minute contact period.
Water obtained from an approved source or distilled in open seas must be chlorinated to 0.2 ppm following a 30-minute contact period.
The free available chlorine level of a ships water supply is checked by the Palin-DPD method. With this method, a tablet is placed in a small test tube filled with water. If chlorine (or bromine for ships having bromine disinfection) is present in the water, a color change will take place as the tablet dissolves. When the tablet is fully dissolved, the color of the sample is compared to color standards furnished with the kit. When a color match is obtained, the disinfectant